About a month ago my travels took me to the National Transportation Museum, (Barretts Station), Saint Louis. While there I made yet another careful inspection of my favorite piece of equipment in their collection: The Milwaukee Road Bi-Polar electric locomotive.
Sneaking around to the northside of this improbable beast I discovered something that quite surprised me. Resting on one of the D-truck wheels was a much smaller idler wheel, the latter being connected to a cable that ran up to the engine cab. I suspect that this unexpected appurtenance was in fact part of the speedometer mechanism.
Checking the opposite side of the locomotive reavealed no such item in place. Either the bi-polars were equipped with only one such device or a second one was removed sometime ago.
On plenty of diesel locomotives I’ve seen speedometer cables connected directly to outside of any one axle, but seeing an idler wheel mechanism being spun by a locomotive tire was quite a surprise.